In the manufacture of glass fibers a molten glass is typically drawn from a precious metal container called a bushing in the art through a plurality of orifices located in the bottom of the container. The container is electrically heated to maintain the glass in it in the molten state. The glass filaments drawn from the orifices are gathered together in strand form and wound on mandrels at high speed to collect a strand product, or they are attenuated in chopping devices which chop the strands into various lengths and which are then packaged and sold as chopped fibers. In the manufacture of shingles utilized for asphalt roofing products glass fibers have begun to enjoy success as the reinforcement material replacing the formerly used organic rag felts and asbestos products which have been used in the past. It has been common practice in the art to use chopped glass fibers to manufacture fibrous glass mats as a replacement for the rag felts and asbestos felts previously employed and in doing this it has also been common practice in the art to utilize glass fibers of varying lengths in a given mix as an aqueous dispersion for the preparation of such fibrous mats. Two patents which typify the art of utilizing fibrous mats having various diameter fibers in the mats and having varying lengths are the inventions described in U.S. Pat. Nos. 4,112,174 and 4,129,674. It has also been described in U.S. Pat. No. 3,749,638 that varying fiber lengths for a given fiber glass diameter may be employed in the utilization of glass fibers for the preparation of glass mats.
In the normal glass fiber producing operation the bushings are generally rectangular or circular shaped containers having a multiplicity of orifices located on the bottom of them. In fabricating the bushings the orifices are controlled in diameter to insure that each orifice is of the same size so that a glass fiber of a given diameter can be produced from that bushing. All of the filaments produced from each of the orifices as the glass is withdrawn from the container thus have precisely the same diameter since they are being attenuated with either a chopping device or a winder at the same speeds for a given bushing temperature. In view of the recent increase in use of glass fibers in the mat making area for roofing products and in view of the fact that mixed filament diameter fibers are being employed in that use, it is desirable to produce in a single bushing a desired product mix of fibers having two different diameters for utilization in producing mat products from these mixed diameter filaments. Thus, there is a need to provide a bushing capable of producing glass fibers which will achieve this result.